The present invention relates to a signal delay circuit utilizing a data memory and, more particularly, to an address control circuit employed in such a signal delay circuit for generating a data write address and a data read address for the data memory.
In recent audio systems, "Acoustic Environment Reproduction" is becoming one of main themes for audio application. Acoustic Environment Reproduction is a process to provide a pseudo acoustic effect for realizing a concert hall's acoustic effect, for example. In order to realize the concert hall's acoustic effect, the reproduction of reverberation sound is required. For this purpose, a signal delay circuit utilizing a data memory is used.
More specifically, an audio signal to be reproduced is converted into and outputted as digital data in a sampling cycle from a compact disk player, for example. The respective digital data are then temporarily written into the data memory by supplying respective data write addresses to the memory. Certain digital data, which has already been written into the data memory, is read out therefrom after a preselected time period by supplying the corresponding data read address to the memory. The read-out digital data is then subjected to a desired type of processing such as a digital filter processing. The reverberation sound data is thereby reproduced. That preselected time period corresponds to a delay time of the reverberation sound. If a plurality of reverberation sound data are necessary at one time, the corresponding digital data, which have already been written into the data memory at different sampling times, are read out therefrom within one sampling cycle.
Thus, as addresses to be supplied to the data memory in each sampling cycle, there are required a data write address for current audio digital data and at least one read data address for reverberation sound data. Each of the data write and read addresses is, in general, calculated and then supplied to the data memory by a program consisting of a string of instructions. On the other hand, in order to realize acoustic environment reproduction, other processes such as a noise reduction, tone control, loudness compensation, stereo image enhancement, etc., are also required in each sampling cycle. These processes are performed by a great number of appropriate digital filtering operations which are in turn controlled by a program. This means that the number of program steps available for controlling the filtering operations is reduced due to the program for calculating and generating the data write and read addresses. For this reason, the realization of the acoustic environment reproduction results in incomplete results.